Our project, supported by this Program Project Grant, has demonstrated that matrilysin serves both beneficial and detrimental functions. On one hand, it is required for efficient airway and alveolar repair, but on the other, it controls neutrophil influx and activation. In the absence of matrilysin, mice survive acute injury much better than do wildtype mice. Thus, matrilysin is an attractive target for intervention. The approaches used to target MMPs rely on nonspecific strategies, resulting in confounding and unexpected side effects. Thus, we propose that understanding how an individual enzyme is controlled will point to mechanisms that can be targeted for treatment. We now plan to explore the molecular mechanism controlling the catalytic activity of matrilysin and its ability to recognize specific substrate by lung epithelial cells in vivo. Our preliminary in, vitro studies suggest that pro-matrilysin is activated by an allosteric mechanism that disrupts the thiol-zinc interaction allowing autolytic, intermolecular cleavage of prodomain. Furthermore, we have determined that certain glycosaminoglycans (GAGs), particularly chondroitin sulfate type E (CSE), specifically and markedly stimulate both allosteric activation of pro-matrilysin and its catalytic activity to physiologic substrates. Our preliminary data also show that airway epithelial cells express serglycin, a CSE proteoglycan found in secretion granules, and in other tissue models, that activation of pro-matrilysin and cleave of matrilysin substrates is impaired in serglycin-null mice. For this project, we hypothesize that a direct interaction between the CSE chains of serglycin and pro-matrilysin within the secretion pathway mediates activation of this MMPs. Thus, this mechanism sits high in hierarchy of events controlling matrilysin-mediated proteolysis. Our aims are to: 1) determine the role of serglycin in the activation of promatrilysin in injured airway and alveolar epithelia; 2) determine how serglycin regulates the substrate specificity of activated matrilysin; and 3) assess the role of matrilysin-mediated catalysis in governing the epithelial response to injury.